Prior art injection molding machines commonly include a large, one piece yoke surrounding the mold sidewalls, the yoke being intended to prevent outward deflection of the mold sidewalls during injection of plastic into the mold cavity. One example of such prior art apparatus is illustrated in the Halsall U.S. Pat. No. 3,509,603, issued May 5, 1970. That patent illustrates an injection mold which includes a yoke integral with one of the mold plates and surrounding a plurality of outwardly moveable sidewalls, the yoke providing support for the sidewalls during the injection process. The construction of a mold such as illustrated in the Halsall patent requires machining of a large block of steel so as to provide a central cavity in the block of steel, the cavity being large enough to house the mold cores and the mold sidewalls. The yoke provides an integral one piece rigid structure completely surrounding the mold cavity and is intended to provide rigidity to prevent any outward deflection of the mold sidewalls.
Attention is also directed to the Lovejoy U.S. Pat. No. 3,930,780, issued Jan. 6, 1976 and showing a mold structure similar to that shown in the Halsall patent and also including a one piece integral yoke having a central bore and surrounding the mold sidewalls. The yoke of Lovejoy is constructed from a thick plate of steel machined so as to form a central cavity, the cavity housing the mold cores and the moveable mold sidewalls.
Attention is also directed to the McDonald U.S. Pat. No. 4,206,799, issued June 10, 1980.
Attention is further directed to the Wilds et al. U.S. Pat. No. 3,473,197 issued Oct. 21, 1969; the Bromley U.S. Pat. No. 3,278,252, issued Dec. 6, 1966; the Lovejoy U.S. Pat. No. 3,905,740, issued Sept. 16, 1975; the Ladney U.S. Pat. No. 3,373,460 issued Mar. 19, 1968 and the Lovejoy U.S. Pat. No. 3,838,960 issued Oct. 21, 1974.
Attention is further directed to the Wilds et al. U.S. Pat. No. 4,278,417; the Amigo U.S. Pat. No. 2,292,593 issued Aug. 11, 1942; the Tucker U.S. Pat. No. 3,534,443, issued Oct. 20, 1970; the Guzzo U.S. Pat. No. 3,865,529, issued Feb. 11, 1975; the Fuke et al. U.S. Pat. No. 4,362,291 issued Dec. 7, 1982; and the Tucker U.S. Pat. No. 3,585,690, issued June 22, 1971.